Altimeter



April 29, 1930. Q F, JENKlNS 1,756,462

l ALTIMETER v Filed April 18, 1924 --H--f-T-- Patented Apr. 29, 1930 UNITED STATES PATENT OFFICE ALTIMETEB Application filed April 18,

This invention relates to that class of apparatus known as altimeters, and' has for its distinguishing feature means for determining the distance to the ground from a iying machine in the air rather than the altitude of the plane above sea-level. l

The usual altimeter' is Worthless when one is flying in mountainous country at night or in fog or snow, as it jgives no warning at all of the approach of a mountain.

The object of this invcntionis to Warn the pilot of the approach of an obstruction, for example, a mount-ain, a forest or the like, and this is accomplished by the employment'of radio Waves propagated in the plane and relected from the obstruction, and the phase relation of the refiected (to the succeeding propagated Wave or Waves at the source.

In the diagrammatic drawings herewith Figs. l, 2 and 3 illustrate the principle involved; and Fig. 4 one method of applying the same. f

In Fig. 4 let S represent a radio sending machine, preferably having pronounced directional characteristics; R a receiving instrument, which may be tuned; and L a lamp lighted by the induction current of a -circuit coil BCI. Any suitable low voltage lamp adapted to the strength of current induced in the secondary or third coil may be employed. Both sending and receiving machines and the lamp are carried on the plane, the lamp perhaps on the instrument board of the plane.

Let it be explained that when the current in the sendino` coil (a) of SCI is in phase with the current from the receiving coil (y) of SCI, that the lamp L will burn at maximum brightness, and that when the current is out of phase the lamp burns less brightly until when it is in opposit-ion the light may go out entirely, a Well known phenomena, of course.

To illustrate the operation of the device it may be assumed that the plane is flying on the line Aw-A, one Wave length above the ground at the moment. With the sending machine in operation, the Wave reiiected from the ground is also one Wave length long.y or a total of two Wave lengths ou its return 50 to thi` plane. wher, it is picked up by the re- 1924. Serial No. 707,408.

'ceiving set. The ,wave frequency in coil `z is` therefore, in phase with the frequency in coil y and the lamp burns brightly. This condi tion is shown in Fig. l.

In Fig. 2 theiplane has advanced to a posi- 55 ltion Where the phase relation has been disturbed by reason of the rising ground M, and the light burns less brightly. Therefore the pilot is warned of a difference in the ground elevation and he noses his plane up. If this makes the lamp burn brighter he is advised that the ground is rising, but alsothat he is rising faster. If the lamp should go out entirely the pilot would be advised that a mountain was rising iirhis path faster than he is climbing, and he would pull his plane up still more sharply 'to maintain a brightly burning lamp, the indication of a safe elevation above the obstruction.

lVhe'n the plane is safely over the obstruc- 70 tion the lamp gets more vdim instead of brighter as the plane continues to rise, and the pilot flattens out.

By changing the Wave lengt-h. of the sending machine by the rotation of the dial f (Fig. 4), and synchronously the dial g on the receiving machine, for example, by means of the belt h, to exactly one Wave length, the height above the ground can be read directly on the dial (assuming the dials to be calibrated in feet).

lVhat I claim, therefore, is

l. A safety device for an airplane for indicating its approach to an obstruction and comprising a sending set carried by the airplane and having pronounced Adirectional characteristics for propagating radio Waves of a length corresponding to the desired flight height of the airplane and adapted to be reflected back by the surface of the ground A to the airplane, a receiving set also carried by the airplane for receiving the reflected radio Waves, and means connected with the sending and receiving `sets for indicating when the propagated and reflected waves are 9-5 in and out of phase.

Q. A safety device for an airplane for indicating its approach to an obstruction and comprising a .sending .set carried by the airplane and having pronounced directional characteristics for propagating radio Waves of a length correspon.flingr to the desired Hight height of the airplane und adapted to he reflected back by the surface of thel ground to the airplane, a receiving' set also carried by the airplane for receiving the relected radio Waves', and means connected with the sending and receiving sets for indicating when the propagated and reflected Waves are in and out of phase, said means in-V cluding a three circuit induction coil having its primary coils connected with the sending and receiving sets, and a lamp connected with the. secondary coil of the third circuit lnduction coil.

In testimony whereof I have aixed my gnat'ure.

CHARLES FRANCIS JENKINS. 

